Not sure about the Petty car but I found this on the Tony Nancy car.
"Finished in blazing orange, the absolutely immaculate, center-steered ’29 Model A roadster was the first of what would be a long line of Nancy’s famed 22 Jr. racing cars. The “22 Jr.†racing number was partly derived from the fact that Nancy favored the number “2â€. Also, since he was competing with a smaller-displacement engine against competitors with much larger engines, he added the “Jr.†suffix."
Tom